Existence of activin-A in A- and D-cells of rat pancreatic islet.

Activin-A, a member of the transforming growth factor-beta supergene family, stimulates insulin secretion in rat pancreatic islets and causes glycogenolysis in isolated rat hepatocytes. These observations prompted us to determine whether activin-A existed in rat pancreas by using an immunocytochemical method. Cells in pancreatic islets were stained by antibody against activin-A, whereas no immunoreactivity was observed in exocrine pancreas. Cells localized in the mantle of the islets were densely stained by the antibody. Immunoelectron microscopic study showed that activin-A existed in secretory granules in both A- and D-cells. Furthermore, studies using a double labeling method revealed that activin-A coexisted with glucagon in secretory granules in A-cells and with somatostatin in D-cells. Antibody against inhibin-A weakly stained cells in both the core and mantle of the islets only when the rat was pretreated with colchicine. Subtypes of activin subunit in islets were identified to be beta A by a rever...